1. Field of the Invention
The present invention relates to a sealed alkaline-zinc storage battery capable of starting with discharge, more particularly to a sealed alkaline-zinc storage battery which exhibits excellent storage characteristics, such as a low degree of deterioration in discharge capacity even after a long-term storage and the reduced occurrence of leakage of electrolyte. The storage battery capable of starting with discharge, as used herein, refers to the storage battery which can start initially with discharging without a need to be charged prior to use.
2. Related Art
In Japanese Patent Publication No. 45-16653 (1970), an alkaline-manganese secondary battery is disclosed which includes manganese dioxide as a depolarizer, zinc as negative active material and an aqueous caustic solution as an electrolyte, and which specifies a total water content of the alkaline electrolyte as being within the range of 0.75-1.10 g relative to 1 g of zinc as the negative active material. In this secondary battery, the water content of the alkaline electrolyte is in the range of 0.92-1.34 g for each theoretical capacity of the negative electrode.
The inventors of the present application have found that the water content range of the alkaline electrolyte specified in the above-identified reference, if applied to a sealed alkaline-zinc storage battery capable of starting with discharge and including nickel hydroxide as a positive active material and zinc as a negative active material, adversely affects the long-term storage characteristics thereof. Specifically, such a storage battery exhibits appreciable deterioration in discharge capacity. With the increased number of charge-discharge cycles, the increasing amount of oxygen gas evolution occurs at the positive electrode to raise an internal pressure of the battery, ultimately causing the electrolyte to leak.